Combat
Use these rules for battles in water or underwater:
- Your speed is halved unless you have a swim speed, in which case you use your full swim speed.
- You gain resistance 5 to acid and fire.
- You take disadvantage to melee attacks that deal bludgeoning or slashing damage that pass-through water.
- Ranged attacks that deal bludgeoning or slashing damage must succeed at a Flat DC 20 if the attacker or target is underwater. All ranged attacks made by an underwater creature or against an underwater target have their range increments halved.
- Wearing medium or heavy armor reduces your speed by half (whether or not you have a swim speed) while underwater. Further, wearing heavy armor increases the DC of any Athletics check made to swim by 10.
- All spells, supernatural abilities, and other abilities that have the fire tag automatically fail.
- At the GM’s discretion, some actions might not work underwater or while floating.
In certain situations, lighting can also be reduced if you are farther underwater.
Drowning
You can hold your breath for a number of rounds equal to 5 + your Constitution modifier. Reduce your remaining air by 1 round at the end of each of your turns or by 2 if you attack or cast any spells that turn. You also lose 1 round worth of air each time you a dealt a critical hit or critically fail a save against an affect the deals damage. If you speak (including casting spells with verbal components) you lose all remaining air.
When you run out of air, you gain the Unconscious condition. You cannot recover from being Unconscious and must attempt a DC 20 Fortitude save at the end of each of your turns. On a failure, you take 1d10 damage, and on a critical failure, you die. On each check after the first, the DC increases by 5 and the damage by 1d10; these increases are cumulative. Once your access to air is restored, you stop suffocating and are no longer Unconscious (unless you’re at 0 Hit Points, in which case the Dying condition is applied still).